Modeling and Analysis of Particulate Matter Deposition and Regeneration in a Diesel Particulate Filter

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Abstract

Diesel engines are widely used because of their high efficiency and low “greenhouse gas” emission. The particulate matter (PM) emitted by a diesel engine is collected and then burned in a diesel particulate filter (DPF). Analysis and modeling works have been done in this research to provide insight on optimization of the DPF design and operating conditions to achieve low pressure drop across the filter to decrease fuel consumption and low peak temperature during regeneration to avoid filter melting, cracking, and/or catalyst deactivation.
Limiting models of the 1-D two-channel DPF model are analyzed. Analytical predictions and physical insight on the filtration velocity, pressure drop, heat transfer, light-off and regeneration in a DPF are obtained. The hydraulic analysis enables an efficient optimization of the DPF that lead to a more uniform PM deposition profile and a decrease of the pressure drop. The heat transfer, light-off and regeneration analysis enable estimations of the DPF heat-up time, the speed and width of the temperature front, the light-off temperature and time, and the peak regeneration temperature. New DPF regeneration procedures are proposed to limit the maximum local temperature rise.
In various cases a DPF is connected by a wide-angled cone (diffuser) to the engine exhaust pipe. A 2-D axisymmetric PM deposition and regeneration model is developed to investigate the impact of the inlet cone on the deposition rate and the regeneration temperature as well as on the transient inlet velocity distribution among the various DPF channels. The highest regeneration temperature and thermal stress when using an inlet cone may be quite higher than when it is absent.
A major technological challenge in the regeneration of the ceramic cordierite filter is that a sudden decrease of the engine load, referred to as Drop to Idle (DTI), may create a transient temperature peak much higher than under either the initial or final stationary feed conditions. This excessive transient temperature rise may cause local melting or cracking of the ceramic filter. Suggestions on how to limit the peak temperature rise following a DTI are provided through numerous simulations of the 1-D and 2-D DPF regeneration models.